You are using the wrong pronoun in your sentences. "You" should not be doing any of it based on the questions you are asking. You should have a "plumber" do those tasks so it is done correctly and permanently.

: I live in a home that was built around 1900. I want to install a bathroom upstairs, directly above the downstairs bathroom. Will there be enough pressure from downstairs to push the water up, or do I need some sort of pump? Second, where do I tie into the existing water supply to take it upstairs? Can this all be done by running it up and down through an exisitng wall?